JP4841662B2 - Magnetic detection device and feedback method of cancel head output thereof - Google Patents

Description

  The present invention relates to a magnetic detection device having a plurality of AC differential magnetic heads and a cancel head output feedback method.

  Traditionally, securities such as banknotes, government bonds, and stamps have been printed using special inks that contain magnetism. In order to check whether the printed matter has a certain quality, Detection has been performed.

  For example, as a technique for detecting the magnetic characteristics of printed matter, Patent Document 1 discloses a plurality of aligned magnetic cores each wound with a primary coil and a secondary coil, a primary coil for cancellation, and a canceling coil. It has a structure in which a cancel core around which a secondary coil is wound and a member that integrally couples a plurality of magnetic cores and a cancel core are arranged so that the detection surface of each magnetic core faces the object to be detected in a row. A multi-channel magnetic head is disclosed.

  According to such a multi-channel type magnetic head, the magnetic core is excited in the same phase using a single oscillation circuit, thereby preventing mutual interference such as howling occurring between a plurality of adjacent magnetic cores. .

Japanese Patent No. 2585558

  However, in the above prior art, while mutual interference by adjacent magnetic heads can be prevented, sensitivity characteristics due to temperature differences between channels, etc., or variations in sensitivity characteristics due to aging and / or aging of components, etc. occur between channels. There is a problem that the magnetic detection signal output from the magnetic head may vary.

  For example, when evaluating the magnetic characteristics of a large-sized printed material as in the printed material inspection apparatus described in Japanese Patent Application Laid-Open No. 2001-001506, the variation in magnetic detection signal between channels becomes particularly significant.

  Specifically, in the printed matter inspection apparatus described above, the detection that the magnetic head faces the large format printed matter can be detected accurately even if the special ink printed on the banknote or the like is undried. While maintaining a certain clearance between the surface and the large-sized printed material, the magnetic characteristics are detected while the roller travels using only the blank portion of the large-sized printed material as the traveling path.

  Here, in such a printed matter inspection device, unevenness occurs on the printed surface of the magnetic ink after printing due to pressurization by a printing machine, etc., so that the clearance is kept constant by pressing the printed surface by blowing air from the magnetic head. Air pressure control is performed.

  As shown in FIG. 6A, the lower surface 90a of the magnetic head 90 is a flat surface parallel to the large-sized printed material that is the object to be detected, and the core 91, the laser emission window 92a, and the light receiving portion are located near the center. A total of six air jets 93 are arranged in a row so as to surround the core 91 on each side in a direction orthogonal to the scanning direction of the magnetic head 90 on both sides. These air jets 93 are connected to a compressed air supply source (not shown) provided in the apparatus main body.

  Then, as shown in FIG. 6B, the laser light emitted from the laser light emission window 92a is reflected by the paper and then received by the sensor through the light reception window 92b, so that the lower surface 90a of the magnetic head 90 and the upper surface of the printed material The gap is measured.

  That is, in the printed matter inspection apparatus described above, the gap between the lower surface 90a of the magnetic head 90 and the upper surface of the printed matter is measured with a laser beam while air is jetted from the air outlet 93 to correct the wavy and wrinkle of the printed matter. The gap is controlled to be kept at a predetermined value (150 μm).

  When such air pressing control is performed, the temperature of the magnetic head and its surroundings change due to the influence of the air temperature, but it is difficult to eliminate such temperature change or to change uniformly between each channel, It will vary in many ways.

  However, in the above-described multi-channel type magnetic head, when the magnetic cores of the channels operate at different temperatures, the difference signal of each channel is only between the magnetic signal of one cancellation core shared by a plurality of magnetic cores. (Magnetic detection signal) cannot be obtained. For this reason, in each channel, the output varies due to the temperature difference between the channels.

  Here, the case where the output varies due to the temperature difference between the channels has been described, but there may be individual differences such as the variation due to the temperature variation characteristic between the magnetic heads and the sensitivity characteristic variation due to secular variation. A similar problem arises.

  Accordingly, the present invention has been made to solve the above-described problems (problems) caused by the prior art, and it is possible to prevent the occurrence of output variations due to temperature differences or individual component differences between channels. It is an object of the present invention to provide a detection device and a feedback method of cancel head output thereof.

  In order to solve the above-described problems and achieve the object, a magnetic detection device according to the present invention includes a plurality of AC differential magnetic heads each having a detection head and a cancel head, and the plurality of AC differential magnetic heads. A single oscillation circuit for exciting each of the AC differential magnetic heads, an excitation coil driving circuit for driving an excitation coil of the AC differential magnetic head, and the excitation coil driving Provided for each circuit, and a feedback circuit for feeding back the output of the cancel head of the AC differential magnetic head corresponding to the excitation coil drive circuit to the excitation coil drive circuit, and the difference between the output of the cancel head and the detection head And a differential amplifier circuit that outputs a dynamic signal.

  In the magnetic detection device according to the present invention as set forth in the invention described above, the feedback circuit includes the cancel head so that the output of the cancel head of each AC differential magnetic head has a predetermined value (including the same). Is fed back to the exciting coil drive circuit.

  According to another aspect of the present invention, there is provided a canceling head output feedback method comprising: an excitation step for in-phase excitation of a plurality of AC differential magnetic heads each having a detection head and a canceling head using a single oscillation circuit; The output of the cancellation head of the AC differential magnetic head corresponding to the excitation coil drive circuit is fed back to the excitation coil drive circuit that is provided for each type magnetic head and drives the excitation coil of the AC differential magnetic head And a differential signal output step of outputting a differential signal of outputs of the cancel head and the detection head.

  According to the present invention, the output amplitude of the cancel head can always be controlled to a predetermined constant value in each channel, and can be controlled to a predetermined constant value among all the channels. There is an effect that it is possible to prevent output variation due to the difference.

  In addition, according to the present invention, magnetic detection can be performed so that the magnetic heads of all channels have the same sensitivity characteristics, and even when the magnetic characteristics of the same object are detected by a plurality of magnetic heads. There is an effect that it is possible to obtain the same detection accuracy as when magnetic detection is performed with one magnetic head.

FIG. 1 is a diagram illustrating a circuit configuration of a head unit according to the present embodiment. FIG. 2 is a diagram illustrating an example of the structure of the magnetic head according to the present embodiment. FIG. 3 is a diagram showing the configuration of a head unit in which the magnetic head is fixed. FIG. 4 is a diagram showing a head unit in which the magnetic head is movable. FIG. 5 is a circuit diagram of a feedback circuit according to the present embodiment. FIG. 6 is a view showing an example of the structure of a magnetic head according to the prior art.

  Exemplary embodiments of a magnetic detection device (hereinafter referred to as a head unit) and a feedback method of a cancel head output according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram illustrating a circuit configuration of a head unit according to the present embodiment. The head unit 1 shown in FIG. 1 is for detecting the magnetic characteristics of an object. For example, large-format printed matter (for example, bills, securities such as government bonds and stamps) printed using special ink containing magnetism. It is suitably mounted on a printed matter inspection apparatus that performs magnetic inspection.

  As shown in FIG. 1, the head unit 1 has a circuit configuration in which a plurality of channels of subsequent circuits are connected to a single oscillation circuit 11. In FIG. 1, only the circuit configuration of 1CH is shown, but 2CH and 3CH also have the same circuit configuration. The number of magnetic heads 30 (the number of CHs) mounted on the head unit 1 can be arbitrarily changed.

  The oscillation circuit 11 is a circuit that generates an AC reference signal and outputs an in-phase AC signal to each subsequent channel, and is configured by, for example, a Wien bridge circuit or an equivalent circuit thereof. As described above, in this embodiment, each magnetic head 30 is excited based on the in-phase AC signal generated by the single oscillation circuit 11.

  That is, when a plurality of magnetic heads 30 are arranged in parallel, a wider range of scanning is possible than when a printed matter is scanned with a single magnetic head. On the other hand, when each magnetic head 30 is excited and driven independently, the AC excitation magnetic field of the adjacent magnetic heads 30 may cause mutual interference, which may cause howling in the output of the magnetic detection signal of each magnetic head.

  Therefore, in this embodiment, the magnetic heads 30 of each channel are excited in phase using the single oscillation circuit 11 to prevent interference due to leakage magnetic flux between the magnetic heads 30. Even when they are provided adjacent to each other, highly accurate magnetic detection is possible.

  As shown in FIG. 1, each channel in the subsequent stage of the oscillation circuit 11 includes the magnetic head 30 shown in FIG. 2, the excitation drive circuit 12, the amplifier circuit 13, the amplifier circuit 14, and the differential amplifier circuit 15. A feedback circuit 50 is provided.

  Here, the magnetic head 30 shown in FIG. 1 will be described with reference to FIG. 2 while exemplifying a configuration of a magnetic head that is preferably applied when detecting the magnetic characteristics of a large-sized printed material.

  The magnetic head 30 is an AC bias type magnetic detection head, and includes a detection surface, that is, a detection head provided on the printed material side, and a cancel head provided on the opposite side to the printed material. Composed. In addition, the magnetic head 30 is provided with an air outlet in the detection surface of the magnetic head 30 and / or in the vicinity of the detection surface in order to correct waviness and wrinkles of the printed matter. In addition, although illustration is abbreviate | omitted here, you may provide an air jet nozzle so that air may be sprayed between a head detection surface and printed matter from a horizontal direction.

  FIG. 2 is a diagram illustrating an example of a magnetic head according to the present embodiment. In the subsequent drawings including FIG. 2, the traveling direction of the head unit 1 (the direction in which the printed product is scanned) is the X axis, the direction orthogonal to the X axis is the Y axis, and the plane includes the X axis and the Y axis. The description will be made with the orthogonal vertical direction as the Z axis.

  As shown in FIG. 2A, an air outlet 31 is provided on the lower surface of the magnetic head 30. In addition, a detection region 32 capable of magnetic detection exists at the center of the lower surface. That is, the area other than the detection area 32 is an insensitive area with respect to magnetism.

  Here, the width 33 of the magnetic head 30 in the Y-axis direction is, for example, 16 mm, and the width 34 of the detection region 32 in the Y-axis direction is, for example, 10 mm. In this embodiment, the case of using the magnetic head 30 having the insensitive area on the outer peripheral portion of the detection surface will be mainly described. However, the magnetic head 30 having the insensitive area minimized may be used.

  As shown in FIG. 2B, a counter electrode core 35 is provided inside the magnetic head 30. In addition, air is blown in the direction 300 from the ejection port 31 provided on the lower surface of the magnetic head 30 toward the large-sized printed matter.

  As shown in FIG. 2C, a cancel head 35 a and a detection head 35 b are configured on the counter electrode core 35. Specifically, in the upper block 35aa of the counter electrode core 35, the cancellation head primary coil 35ab is wound around the excitation drive circuit 12 side pole, and the cancellation head secondary coil 35ac is wound around the amplification circuit 13 side pole. Thus, a cancel head 35a is configured.

  Further, the detection head primary coil 35bb is wound around the excitation drive circuit 12 side pole of the lower block 35ba of the counter electrode core 35, and the detection head secondary coil 35bc is wound around the pole on the amplification circuit 14 side. A head 35b is configured.

  Thus, the primary coils 35ab and 35bb of each of the upper and lower blocks are connected in series, and the secondary coils 35ac and 35bc of each of the upper and lower blocks are connected in parallel.

  The AC reference signal generated by the oscillation circuit 11 is input to the excitation drive circuit 12 through feedback by a feedback circuit 50 described later. Subsequently, the excitation drive circuit 12 adds a predetermined excitation signal to the reference signal, and then energizes the cancel head primary coil 35ab and the detection head primary coil 35bb. Thereby, an alternating magnetic field is generated. Thereafter, the secondary coil 35ac for the cancel head and the secondary coil 35bc for the detection head detect a change in the alternating magnetic field due to the approach of the magnetic body.

  At this time, the secondary coil 35bc for the detection head detects a change in the alternating magnetic field due to the magnetic ink printed on the printed material. However, the secondary coil 35ac for the cancel head detects the change in the alternating magnetic field because it is separated from the printed material. Do not detect.

  Therefore, a signal obtained by amplifying the output from the cancel head secondary coil 35ac by the amplifier circuit 13 and a signal obtained by amplifying the output from the detection head secondary coil 35bc by the amplifier circuit 14 are input to the differential amplifier circuit 15. Thus, a magnetic signal (difference signal) based on the output of the cancel head 35a can be acquired.

  Next, the arrangement configuration of the magnetic head 30 in the head unit 1 will be described with reference to FIGS. FIG. 3 is a diagram showing a configuration of the head unit 1 in which the magnetic head 30 is fixed.

  As shown in FIG. 3, when using the magnetic head 30 with the smallest dead area, the magnetic heads 30 may be arranged adjacent to each other in the Y-axis direction of the head unit 1. In this way, when the head unit 1 is moved in the scanning direction 200 to scan a large-sized printed material, a wider range of magnetic information can be obtained by one scan.

  Here, the interval 36 between the pair of rollers 30b provided so as to travel in the scanning direction 200 is adjusted to a width through which each roller 30b passes over the margin between the print originals printed on the large-format print. . Further, the width 37 of each roller 30b is adjusted to be smaller than the width of the margin.

  Although FIG. 3 shows the head unit 1 having one set of rollers 30b, the head unit 1 having a plurality of sets of rollers 30b may be configured. For example, although not shown, three sets of rollers 30b can be arranged, and the magnetic head 30 can be arranged for each mounting shaft. As described above, if a plurality of sets of rollers 30b are arranged, it is possible to prevent a pitching operation (rotating operation around the Y axis) when the head unit 1 moves in the scanning direction 200.

  Further, as shown in FIG. 3, when a plurality of magnetic heads 30 are fixed in the head unit 1, a scanning area required for the width in the Y-axis direction of one line of a large-sized printed material in one scan is obtained. A comprehensive number of magnetic heads 30 may be provided. Further, after the roller 30b is omitted, the scanning may be repeated while the head unit 1 is shifted in the Y-axis direction.

  FIG. 3 shows the case where a plurality of magnetic heads 30 are fixed in the head unit 1, but the head unit 1 in which the magnetic head 30 is provided so as to be movable in the Y-axis direction may be configured. Therefore, hereinafter, the head unit 1 in which the magnetic head 30 is movable will be described with reference to FIG.

  FIG. 4 is a diagram showing the head unit 1 in which the magnetic head 30 is movable. Note that (A) in the figure shows a case where two magnetic heads 30 arranged at a predetermined interval in the Y-axis direction are moved.

  As shown in FIG. 4A, the two magnetic heads 30 are fixed to the movable portion 42 so that the distance between the detection regions 32 has a predetermined width 41. The movable portion 42 is driven by a motor (not shown) and controlled to move in a direction 43 that is the negative direction of the Y axis and a direction 44 that is the positive direction of the Y axis.

  The motor that drives the movable unit 42 operates in accordance with an instruction from the control unit of the printed matter inspection apparatus (not shown). Then, the head unit 1 moves in the scanning direction 200 while fixing the position of the movable portion 42 in the Y-axis direction, and when performing the next scanning, the position of the head unit 1 in the Y-axis direction is fixed, Only the movable part 42 is shifted along the Y axis.

  For example, as shown in FIG. 4A-1, in the first scan of a predetermined print original image 101 included in the large-format print, the area indicated by the diagonal lines in FIG. Magnetic information is acquired. Then, when the second scanning is performed with only the movable portion 42 shifted in the positive direction of the Y axis while the position of the head unit 1 in the Y axis direction is fixed, a diagonal line is shown in FIG. The magnetic information of the area is acquired.

  In this way, even when there is a dead area in the magnetic head 30, magnetic information over the entire printing original image 101 printed on each line of the large format printed matter is acquired without changing the position of the head unit 1 in the Y-axis direction. can do. 4A illustrates the case where two magnetic heads 30 are used, the number of magnetic heads 30 may be three or more.

  Here, the present embodiment is characterized in that a feedback circuit 50 for feeding back the output from the cancel head secondary coil 35ac of each magnetic head 30 to the corresponding CH excitation drive circuit 12 via the amplifier circuit 13 is provided. There is.

  That is, when air press control is performed on a printed matter with the printed matter inspection apparatus described above, the temperature of the counter electrode core 35 and its surroundings changes under the influence of the air temperature, but the temperature change is completely between channels. In many cases, the temperature changes to a different temperature, resulting in a temperature difference between the channels.

  Also in various components mounted on the head unit 1, such as the primary coil 35ab and secondary coil 35ac for the cancel head, the primary coil 35bb and secondary coil 35b for the detection head, and the excitation drive circuit. In some cases, individual differences in parts occur between the channels.

  If these temperature differences or individual differences exist between the channels, the output of the cancel head secondary coil 35ac to be a reference also varies between the channels.

  Therefore, in this embodiment, the output of the cancel head secondary coil 35ac is fed back to the excitation drive circuit 12 in each channel, and then the output amplitude of the cancel head 35a is set to a predetermined constant value, and all the channels are set. The amplitude value was the same between the two.

  The feedback circuit 50 will be specifically described with reference to FIG. FIG. 5 is a circuit diagram of a feedback circuit according to the present embodiment. Here, the flow of signals will be described with reference to FIG. 5 focusing on input / output to the three operational amplifiers 51 to 53 in the figure. Note that the VR shown in FIG. 5 may have a circuit configuration in which one VR is provided for all channels.

  As shown in FIG. 5, the operational amplifier 51 is incorporated in the feedback circuit 50 as a buffer amplifier, and the input terminal + has an AC reference excitation waveform from a CP (connection point) 01 connected to the oscillation circuit 11. Is entered.

  In this operational amplifier 51, the AC signal from CP01 is one-way in the direction of the operational amplifier 52 to separate the subsequent circuit from the previous oscillation circuit 11, and to prevent the previous oscillation circuit 11 from being affected by the influence of the subsequent circuit. It is out.

  The operational amplifier 52 is incorporated in the feedback circuit 50 as a non-inverting amplifier, and operates so as to keep the output stable by negative feedback to the input terminal −, and the alternating current output by the operational amplifier 51 is connected to the input terminal +. An FET driven by a reference signal (reference excitation waveform) and an output voltage output from the operational amplifier 53 is connected, and a resistance value between the input terminal + of the operational amplifier 52 and GND is changed.

  The operational amplifier 53 is incorporated in the feedback circuit 50 as a differential amplifier, and the constant power supply voltage between VCC and VEE is divided at the input terminal + so that it becomes a predetermined target voltage value by a variable resistor. The output amplitude signal of the cancel head secondary coil 35ac is input to the input terminal − via the amplifier circuit 13 and CP11.

  In the operational amplifier 53, the difference between the target voltage value input to the input terminal + and the output amplitude input to the input terminal − is amplified with a constant differential gain and output from the output terminal.

  Here, the target voltage value input to the input terminal + of the operational amplifier 53 is a target value for converging the output amplitude of the cancel head 35a to a constant value, and the output amplitude of each cancel head 35a is led to the same target value. Therefore, a common value is set between all channels. The target voltage value can be arbitrarily set by changing the resistance value of the variable resistor.

  As described above, if a target value for converging the output amplitude of the cancel head 35a to a constant value is set as a voltage value to be input to the input terminal + of the operational amplifier 53, and the target value is made common among all channels, The output amplitude of all the cancel heads 35a can be made the same as the set value.

  That is, when the output amplitude of the cancel head 35a is higher than the target voltage value, the amplitude of the excitation waveform output to the excitation drive circuit 12 via the CP 21 is made lower than the amplitude of the reference excitation waveform. The output of the operational amplifier 52 can be controlled so that the output amplitude of the subsequent cancel head 35a approaches the target voltage value.

  When the output amplitude of the cancel head 35a is lower than the target voltage value, the amplitude of the excitation waveform output to the excitation drive circuit 12 via the CP 21 is made higher than the amplitude of the reference excitation waveform. The output of the operational amplifier 52 can be controlled so that the output amplitude of the subsequent cancel head 35a approaches the target voltage value.

  The amplitude of the excitation waveform output from the output terminal of the operational amplifier 52 decreases the amplitude of the excitation waveform if the output value of the cancel head 35a is larger than the target voltage value (large amplitude). If the output value is smaller than the target voltage value (small amplitude), the amplitude of the excitation waveform is increased. That is, control is performed so as to match the determined value.

  As described above, according to the present embodiment, the output of the cancel head secondary coil 35ac is fed back to the excitation drive circuit 12 in each channel. For example, the output amplitude of the cancel head 35a in each channel. Can be controlled to a constant value at all times, and the amplitude value that is constant between all channels can be controlled to any value including the same, and output variations due to temperature differences and individual differences among parts can be controlled. It is possible to prevent it from occurring.

  Further, according to the present embodiment, the output amplitude of the cancel head secondary coil 35ac is fed back to the excitation drive circuit 12 so that the output amplitude of all the cancel head secondary coils 35ac have the same value. Therefore, magnetic detection can be performed so that the magnetic heads of all the channels have the same sensitivity characteristics, and even when detecting the magnetic characteristics of the same object with a plurality of magnetic heads, a single magnetic head can be used. It is possible to obtain detection accuracy equivalent to that obtained when magnetic detection is performed.

  Further, according to the present embodiment, the magnetic heads 30 of the respective channels are configured to be in-phase excited using the single oscillation circuit 11, so that even if the magnetic heads 30 are arranged adjacent to each other, The influence of the alternating magnetic field generated by the magnetic head 30 can be eliminated, and highly accurate magnetic detection can be performed.

  In the printed matter inspection apparatus on which the head unit 1 according to this embodiment is mounted, a correction signal value that eliminates the influence of temperature change can be acquired based on the magnetic detection signal acquired by the magnetic head 30. Configured.

  Specifically, if the temperature of the magnetic head 30 does not change in the scanning section (the section from the scanning start position to the operation end position), the signal value corresponding to the non-magnetic portion should be constant. In this case, the base curve indicating the output voltage of the differential amplifier circuit 15 is a straight line parallel to the time axis.

  However, when air is blown from the detection surface of the magnetic head 30 toward the large-sized printed matter, the temperature difference of the magnetic head 30 due to the blown air blown back on the printing surface is from the magnetic head detection surface to the inside of the head. It takes a predetermined time to reach the thermal equilibrium state by being propagated. Therefore, the balance between the output values of the amplifier circuits 13 and 14 is lost due to the fluctuation of the electrical resistance value due to the heat of the cancel head and the detection head, and the shape of the base curve does not become a straight line. If such a base curve can be obtained, a signal value excluding the influence of temperature change can be obtained by performing correction for subtracting the base curve from the fluctuation curve when the printed material is measured at this time.

  For this reason, in the printed matter inspection apparatus, such a base curve is calculated as an approximate curve by a multidimensional function. Then, the printed matter inspection apparatus obtains a correction signal value that eliminates the influence of the temperature change by subtracting the previously calculated approximate curve from the fluctuation curve of the printed matter magnetic data obtained by the magnetic head 30.

  As a result, in the printed matter inspection apparatus, even when there is a temperature change of the magnetic head in the section from the start of scanning to the end of scanning, it is possible to obtain a signal value excluding the influence of the temperature change. For this reason, it is possible to perform magnetic inspection of large-sized printed matter at high speed without wasting the period until the temperature change of the magnetic head is in a thermal equilibrium state as an inspection standby period.

  In the above embodiment, the circuit diagram shown in FIG. 5 is illustrated as the feedback circuit 50. However, the present invention is not limited to this, and a part or all of the circuit shown in FIG. It may be replaced with a circuit.

  As described above, in this embodiment, output variations due to temperature differences or individual differences among parts can be prevented, so that a plurality of magnetic heads 30 can be freely arranged adjacent to each other.

  For example, when the casing of the magnetic head 30 is a rectangular parallelepiped or a cube, and the detection surfaces of the plurality of magnetic heads 30 are arranged on the same plane, the arbitrary faces of the casing of the magnetic head 30 can be connected and arranged. . As an example, an arbitrary number of magnetic heads 30 can be arranged in parallel or in a zigzag pattern.

  In the present invention, the detection surfaces of the plurality of magnetic heads 30 are not necessarily arranged on the same plane, and the respective detection surfaces can be arranged on different planes.

  As described above, the magnetic detection device and the cancel head output feedback method according to the present invention are suitable for preventing output variations due to temperature differences or individual differences between channels.

DESCRIPTION OF SYMBOLS 1 Head unit 11 Oscillation circuit 12 Excitation drive circuit 13 Amplification circuit 14 Amplification circuit 15 Differential amplifier circuit 30 Magnetic head 35 Counter electrode core 35a Cancel head 35b Detection head 50 Feedback circuit

Claims (3)

A plurality of AC differential magnetic heads each having a detection head and a cancellation head;
A single oscillation circuit for exciting the plurality of AC differential magnetic heads in the same phase;
An excitation coil drive circuit that is provided for each of the AC differential magnetic heads and drives an excitation coil of the AC differential magnetic head;
A feedback circuit that is provided for each excitation coil drive circuit and feeds back the output of the cancel head of the AC differential magnetic head corresponding to the excitation coil drive circuit to the excitation coil drive circuit;
A magnetic detection device comprising: the cancel head; and a differential amplifier circuit that outputs a differential signal output from the detection head. The feedback circuit includes:
2. The magnetic detection device according to claim 1, wherein the output of the cancel head is fed back to the exciting coil drive circuit so that the output of the cancel head of each AC differential magnetic head has the same value. An excitation process for in-phase excitation of a plurality of AC differential magnetic heads each having a detection head and a cancellation head using a single oscillation circuit;
A cancellation head of an AC differential magnetic head corresponding to the excitation coil drive circuit, provided for each of the AC differential magnetic heads and driving an excitation coil drive circuit of the AC differential magnetic head. A feedback process for feeding back the output of
A cancellation signal output feedback method, comprising: a differential signal output step of outputting a differential signal of the output of the cancellation head and the detection head.

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